Method for supplying gas for plasma based analytical instrument

ABSTRACT

To achieve an effective gas filtering in a plasma spectrometric apparatus using a gas of a comparatively high consumption flow rate, and to improve the analytical ability, there is provided a plasma spectrometric apparatus containing a sample introducer for producing and delivering an injector gas containing an analyte sample, a plasma generator for generating plasma into which the injector gas is introduced, and an analyzer disposed subsequent to the plasma generator for analyzing the analyte sample. The plasma spectrometric apparatus contains a first gas line for supplying gas to the sample introducer, a second gas line for supplying gas to the plasma generator, and a filter located in the first gas line for removing impurities contained in the gas.

RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. 119 of JapanesePatent Application No. 2016-15106, filed Jan. 29, 2016, titled “METHODOF GAS SUPPLYING FOR PLASMA BASED ANALYTICAL INSTRUMENT,” the content ofwhich is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a plasma spectrometric apparatusincluding: an ICP analytical apparatus such as an ICP-MS (InductivelyCoupled Plasma—Mass Spectrometry) apparatus and an ICP-AES (InductivelyCoupled Plasma—Atomic Emission Spectrometry) apparatus; and a MIPanalytical apparatus such as a MIP-MS (Microwave Induced Plasma—MassSpectrometry) apparatus and a MIP-AES (Microwave Induced Plasma—AtomicEmission Spectrometry) apparatus. More specifically, the presentinvention relates to a plasma spectrometric apparatus having a devicefor effectively purifying and supplying gas.

BACKGROUND

A plasma spectrometric apparatus such as an ICP or MIP analyticalapparatus is particularly useful for detecting a trace amount ofinorganic elements, and widely used in many fields includingsemiconductor, geological and environmental industries. For purposes ofsimplification, below is provided an explanation of an ICP-MS apparatusas an example of the plasma spectrometric apparatus of the prior art.FIG. 7 shows an example of a configuration similar to the conventionalinductively coupled plasma mass spectrometer (ICP-MS apparatus) shown inFIG. 3 of Patent Literature 1.

In FIG. 7, the flow rate of gas, e.g., an argon gas 704, from a gassource (not shown) is controlled by a gas flow rate control part 703. Acarrier gas from the gas flow rate control part 703 and a liquid sample702 from a sample tank 701 are introduced to a nebulizer 705, and thesample 702 is nebulized. A spray chamber 706 is installed to thenebulizer 705 through an end cap 707. In addition, a make-up gas fromthe gas flow rate control part 703 is supplied to the spray chamber 706through the end cap 707. Of droplets of the nebulized sample 702,droplets with a large particle diameter are attached to an inner wall ofthe spray chamber 706 and dropped, and drained to the outside from adrain hole 706 a. The liquid drained from the drain hole 706 a is sentto a drain tank 708 through a pump 715.

The sample nebulized in the spray chamber 706, and a mixed gas of thecarrier gas and the make-up gas from the gas flow rate control part 703,that is, a gas generally-called an injector gas, are introduced to aplasma torch 709. The plasma torch 709 has a triple-tube structureincluding an inner tube to which the injector gas is introduced, anouter tube that is outside thereof, and an outermost tube that isfurther outside thereof. To the outer tube, an auxiliary gas from thegas flow control part 703 is introduced, and to the outermost tube, aplasma gas from the gas flow rate control part 703 is introduced. Byinductively coupled plasma (ICP) 712 generated by a work coil 711 towhich an electric current from a high frequency power source 710 issupplied, the sample 702 is ionized. Then, in a mass analyzer 713,elements in the ionized sample are separated and detected based on themass-to-charge ratio, and the elements in the sample 702 and eachelement concentration are eventually obtained.

As a result of many years of technological development, it has becomepossible for ICP-MS apparatuses to detect a wide variety of elements ata more minute level. For example, it has become possible for ICP-MSapparatuses to quantify element concentrations at an excellentsensitivity level of one billionth (parts per billion, or ppb) or onetrillionth (parts per trillion, or ppt), and a trace amount of silicon(Si), sulfur (S) or phosphorus (P), etc. contained in an analyte is alsoanalyzed by mass spectrometry.

For example, Non-Patent Literatures 1-4 describe, respectively,performing mass spectrometry of a trace amount of silicon in an organicmaterial such as polyamide; performing mass spectrometry of a traceamount of silicon in a metal material such as steel; performing massspectrometry of a trace amount of silicon in a semiconductor such asGaAs semiconductor; and performing mass spectrometry of a trace amountof silicon contained in water such as ultrapure water. Further,Non-Patent Literatures 5-8 describe, respectively, performing massspectrometry of sulfur or phosphorus contained in organic materials, oilproducts, pharmaceutical products, food, water, biofuels, metalmaterials, biological samples, high-purity reagents, geologicalmaterials, organic solvents, and others; performing mass spectrometry ofa trace amount of sulfur in a semiconductor such as GeO₂; performingmass spectrometry of a trace amount of sulfur in an organic materialsuch as Bisphenol A; and performing mass spectrometry of a trace amountof sulfur in organic matrices such as fuels, biomaterials, andpharmaceutical products.

PRIOR ART DOCUMENTS Patent Literatures

-   Patent Literature 1: Japanese Patent Laid-Open Publication No.    H11-34470-   Patent Literature 2: Japanese Patent Examined Publication No.    H7-4503 (or U.S. Pat. No. 4,795,482)-   Patent Literature 3: Japanese Patent Laid-Open Publication No.    2014-183019-   Patent Literature 4: Japanese Patent Laid-Open Publication No.    2013-143196

Non-Patent Literatures

-   Non-Patent Literature 1: M. Resano, M. Verstraete, F. Vanhaeck    and L. Moens, “Direct determination of trace amounts of silicon in    polyamides by means of solid sampling electrothermal vaporization    inductively coupled plasma mass spectrometry,” Journal of Analytical    Atomic Spectrometry, 2002, 17, 897-903, Published on May 1, 2002    (online)-   Non-Patent Literature 2: Hui-tao Liu and Shiuh-Jen Jiang, “Dynamic    reaction cell inductively coupled plasma mass spectrometry for    determination of silicon in steel,” Spectrochimica Acta Part B:    Atomic Spectroscopy, Volume 58, Issue 1, 1 January 2003, Pages    153-157-   Non-Patent Literature 3: Klaus G. Heumann, “Isotope-dilution ICP-MS    for trace element determination and speciation: from a reference    method to a routine method?” Analytical and Bioanalytical Chemistry,    January 2004, Volume 378, Issue 2, pp 318-329-   Non-Patent Literature 4: Yuichi Takaku, Kimihiko Masuda, Takako    Takahashi and Tadashi Shimamura, “Determination of trace silicon in    ultra-high-purity water by inductively coupled plasma mass    spectrometry” Journal of Analytical Atomic Spectrometry, 1994, 9,    Pages 1385-1387-   Non-Patent Literature 5: J. Giner Martinez-Sierra, O. Galilea San    Blas, J. M. Marchante Gayon, J. I. Garcia Alonso, “Sulfur analysis    by inductively coupled plasma-mass spectrometry: A review,”    Spectrochimica Acta Part B: Atomic Spectroscopy, Volume 108, 1 June    2015, Pages 35-52-   Non-Patent Literature 6: Matti NIEMELA, Harri KOLA and Paavo    PERAMAKI, “Determination of Trace Impurities in Germanium Dioxide by    ICP-OES, ICP-MS and ETAAS after Matrix Volatilization: A Long-run    Performance of the Method,” Analytical Sciences, Vol. 30, Pages    735-738, Published on Jul. 10, 2014 (online)-   Non-Patent Literature 7: M. Resano, M. Verstraete, F. Vanhaecke, L.    Moens and J. Claessens, “Direct determination of sulfur in Bisphenol    A at ultratrace levels by means of solid sampling-electrothermal    vaporization-ICP-MS,” Journal of Analytical Atomic Spectrometry,    2001, 16, Pages 793-800, Published on Jul. 12, 2001 (online)-   Non-Patent Literature 8: Lieve Balcaen, Glenn Woods, Martin Resano    and Frank Vanhaecke, “Accurate determination of S in organic    matrices using isotope dilution ICP-MS/MS,” Journal of Analytical    Atomic Spectrometry, 2013, 28, Pages 33-39, Published on Nov. 12,    2012 (online)

SUMMARY

To address the foregoing problems, in whole or in part, and/or otherproblems that may have been observed by persons skilled in the art, thepresent disclosure provides methods, processes, systems, apparatus,instruments, and/or devices, as described by way of example inimplementations set forth below.

Problem to be Solved by the Invention

When various elements can be detected at a more minute level asdescribed above, it becomes necessary to consider an extremely traceamount of impurities contained in gas used in an ICP-MS apparatus. Asthe gas 704 supplied to the ICP-MS apparatus, gas sold by a gas provideras an industrial gas and the like is generally used, and in some cases,a self-produced industrial gas is used in a facility using an ICP-MSapparatus. These industrial gases can contain an acceptable, extremelytrace amount of impurities. However, as ICP-MS apparatuses come to beable to detect components of a finer level, problems affecting analysisresults can occur, such as detection of these impurities in the massanalyzer 713 as a background noise or occurring of interference by ionsdue to such impurities. In addition, even when the amount of impuritiescontained in the above industrial gases is extremely small, a traceamount of contamination attributed to piping or materials of otherroutes delivering the gases and others may occur and cause similarproblems.

Here, in order to verify the impact of an extremely trace amount ofimpurities contained in gas on an analysis result in a plasmaspectrometric apparatus, the amount of Si in an argon gas (volume ratio)is calculated assuming that Si of 1 ppb (1 μg/L) contained in a liquidsample as an impurity is introduced not from the sample but as theimpurity in the dry argon gas constituting an injector gas. For aconvenience sake, discussion is done by assuming that one Si atom iscontained in one molecule of the impurity. It is assumed that all thegas flow rates (SLM: Standard Litter per Minute) are in a standard state(STP: 273.15K, 0.1 MPa), and the flow rate of the injector gas is 1.07SLM, and the solution suction rate of the nebulizer is 0.2 g/minute (200μL/min). In addition, the passage rate of the nebulized sample in thespray chamber is 5%. As a result, the amount of silicon introduced toplasma at the time of introducing 1 ppb solution is calculated as1.00×10⁻¹¹ (g/min). By converting the unit of the amount of siliconintroduced (g/min) and the unit of the flow rate of the dry argon gas(SLM) to (mol/min) and then performing the above calculation, the Siconcentration in the gas can be obtained in a molar ratio volume ratio),and approximately 7.6 pptv is obtained as the Si concentration in thegas. In other words, when a Si impurity is contained in an amount of 7.6pptv in an argon gas under the above condition, even if a samplesolution does not contain Si, an analysis result is obtained thatindicates that the sample contains 1 ppb of Si. Actually, an argon gasof 99.999% purity may contain a Si impurity of approximately 0.4 ppmv atmaximum.

Conventionally, there was a case of using a gas purifying substance asdescribed in Patent Literature 2, e.g., a filter using zeolite, in a gasline for analytical equipment using gas of comparatively low consumption(flow rate) (≤2 SLM). However, in order to remove impurities containedin the gas 704 supplied to a conventional ICP-MS apparatus such as thatshown in FIG. 7, it is not appropriate, or at least not preferable, touse a conventional filter as-is. The reason is that, while the flow rateof gas supplied to a plasma spectrometric apparatus is generallyapproximately 20 SLM, which is high, the higher the gas flow rate, theshorter the contact time between the gas and the filter, which causesthe gas to pass through the filter without impurities being sufficientlyremoved. It may be possible to produce a filter capable of supporting ahigher flow rate, but the filter becomes much larger, and the cost alsoincreases. Therefore, in a plasma spectrometric apparatus using gas, itis desirable to efficiently remove an extremely trace amount ofimpurities in the gas without increasing a load on a gas filter.

The object of the present invention is to achieve an effective gasfiltering for efficiently removing the above-mentioned extremely traceamount of impurities in a plasma spectrometric apparatus using gas, andto improve the analytical ability of a system.

Means to Solve the Problem

According to the present invention, there is provided a plasmaspectrometric apparatus containing a sample introducer for producing anddelivering an injector gas containing an analyte sample, a plasmagenerator for generating plasma into which the injector gas isintroduced, and an analyzer disposed subsequent to the plasma generatorfor analyzing the analyte sample. The plasma spectrometric apparatuscontains a first gas line for supplying gas to the sample introducer, asecond gas line for supplying gas to the plasma generator, and a filterlocated in the first gas line for removing impurities contained in thegas.

According to one aspect of the present invention, a first gas line and asecond gas line can be configured to be branched or divided from asingle source gas line so that the same gas is supplied. The flow ratethrough the first gas line is smaller than the flow rate through thesecond gas line, for example, by approximately from 6 SLM to 23 SLM, andpreferably by from 11 SLM to 19 SLM.

A filter applied in the present invention can be any of a variety offilters which can effectively remove impurities in gas, and an examplethereof can be a gas purifier for inline piping.

The first gas line can contain a gas flow rate controller between thesample introducer and the filter, in which case, along the gas flow ofthe first gas line, the filter is disposed upstream relative to the gasflow rate controller. However, the filter can also be disposeddownstream relative to the gas flow rate controller. In addition, thegas flow rate controller can also be provided in other gas lines. Thegas flow rate controller can be a mass flow controller.

According to another aspect of the present invention, the sampleintroducer can contain a nebulizer for producing the injector gas bymixing the analyte sample with the gas from the first gas line. Thefirst gas line is branched or divided into a third gas line and a fourthgas line through a connector, and a part of the filtered gas and theremaining part thereof can be delivered to the sample introducer as acarrier gas and a make-up gas, respectively. The nebulizer mixes aliquid sample containing the analyte sample with the carrier gas andnebulizes the resultant mixture, at which time the make-up gas passesthrough an outer surface of a nozzle of the nebulizer to assist thedelivery of the nebulized sample. The filter can also be provided ineach of the third gas line and the fourth gas line instead of the firstgas line.

The filter which can be a gas purifier can be in a form of a cartridgeas an example, and replaceably connected to the first gas line or thethird and the fourth gas lines. The second gas line is branched ordivided into a fifth gas line and a sixth gas line through a connector,and a part of the gas passing through the second gas line and theremaining part thereof can be delivered to the plasma generator as aplasma gas and an auxiliary gas, respectively.

Instead of the sixth gas line, a seventh gas line for delivering theauxiliary gas to the plasma generator may be branched from the first gasline subsequent to the filter. The seventh gas line can be branched, forexample, from the connector at which the third gas line and the fourthgas line are branched.

Additionally, an eighth gas line for delivering a dilution gas to thesample introducer may be branched from the first gas line subsequent tothe filter. The eighth gas line can, for example, be branched from theconnector at which the third gas line and the fourth gas line arebranched. The gas flow rate controller can be provided in each of thethird to the eighth gas lines, and the gas flow rate controller can be amass flow controller.

The plasma generator can contain a plasma torch of triple-tube structurefor receiving the injector gas containing a mixture of the gas from thefirst gas line and the analyte sample, that is, normally a mixture ofthe carrier gas and the make-up gas from the third and the fourth gaslines and the analyte sample, and for receiving the gas from the secondgas line, that is, normally the plasma gas and the auxiliary gas fromthe fifth and the sixth gas lines, to generate plasma for atomizing,exciting, or ionizing the sample. The plasma gas and the auxiliary gascan be delivered to the outermost tube and the outer tube of the plasmatorch, respectively, while the injector gas can be introduced to theinner tube of the plasma torch. The injector gas can also be an outputfrom a gas chromatograph or a laser ablation device.

According to yet another aspect of the present invention, an optionalgas line for supplying an option gas to the sample introducer and asecond filter provided in the optional gas line for removing impuritiescontained in the gas can further be included. The option gas can be anoxygen-containing gas selected from the group consisting of oxygen,argon-containing oxygen, nitrogen-containing oxygen, helium-containingoxygen, and mixtures thereof. The gas supplied through each of the firstand the second gas lines can be selected from the group consisting ofargon, nitrogen, helium, hydrogen, and mixtures thereof.

The apparatus of the present invention can also be described from anaspect of a method. According to this aspect, the present invention isprovided, in a plasma spectrometric apparatus including a sampleintroducer for producing and delivering an injector gas containing ananalyte sample; a plasma generator for generating plasma into which theinjector gas is introduced; and an analyzer disposed subsequent to theplasma generator for analyzing the analyte sample, as a method forreducing background intensity in measurements. The method includessupplying a first gas to the sample introducer through a filter forremoving impurities; and supplying a second gas to the plasma generatorwithout filtering. The first gas is supplied to the sample introducerthrough the first gas line of the plasma spectrometric apparatus. Inaddition, the second gas is supplied to the plasma generator through thesecond gas line of the plasma spectrometric apparatus described above.

The present invention is applicable to an inductively coupled plasmamass spectrometer, an inductively coupled plasma atomic emissionspectrometer, a microwave induced plasma mass spectrometer, a microwaveinduced plasma atomic emission spectrometer, and the like, as long as itis a plasma spectrometric apparatus in which an injector gas containingan analyte sample is produced using gas from a gas source, and theinjector gas is introduced to plasma to analyze the analyte sample.

Effect of the Invention

According to the present invention, in a plasma spectrometric apparatussuch as an ICP-MS apparatus, an ICP-AES apparatus, a MIP-MS apparatus,and a MIP-AES apparatus, it is configured to filter only the gasconstituting the injector gas such as the carrier gas and/or the make-upgas. This reduces background noise attributed to impurities compared toa conventional system, and improves the analytical ability of thesystem. In addition, as a load on the filter is low compared to a casewhere all the supplied gases are collectively filtered, it is possibleto effectively filter the carrier gas and the make-up gas and otherswithout causing the reduction in the filter's removing capability, andthus to prolong the life of the filter.

Other devices, apparatus, systems, methods, features and advantages ofthe invention will be or will become apparent to one with skill in theart upon examination of the following figures and detailed description.It is intended that all such additional systems, methods, features andadvantages be included within this description, be within the scope ofthe invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood by referring to the followingfigures. The components in the figures are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention. In the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 is a schematic drawing showing a configuration example of anICP-MS apparatus according to the present invention.

FIG. 2A is a schematic drawing showing an alternative configurationexample of the ICP-MS apparatus shown in FIG. 1.

FIG. 2B is a schematic drawing showing an alternative configurationexample of the ICP-MS apparatus shown in FIG. 1.

FIG. 3 is a schematic drawing showing a gas chromatograph which can bereplaced with a sample introducer of the ICP-MS apparatus shown in FIG.1.

FIG. 4 is a schematic drawing showing a laser ablation apparatus whichcan be replaced with a sample introducer of the ICP-MS apparatus shownin FIG. 1.

FIG. 5 is a graph showing a removing capability of a gas filter relativeto a flow rate.

FIG. 6A is a graph showing a result of an analysis on successivechronological changes when not using a gas filter (not applying thepresent invention) in an ICP-MS apparatus.

FIG. 6B is a graph showing a result of an analysis on successivechronological changes when using a gas filter (applying the presentinvention) in an ICP-MS apparatus.

FIG. 6C is a bar graph showing the average values of the analysisresults of FIGS. 6A and 6B (BEC value of Si).

FIG. 7 is a schematic drawing showing a configuration example of aconventional ICP-MS apparatus.

DETAILED DESCRIPTION

FIG. 1 shows, as an example of a plasma spectrometric apparatusaccording to the present invention, a configuration of an inductivelycoupled plasma mass spectrometer (ICP-MS apparatus) 100. In FIG. 1, aninjector gas containing fine droplets of a liquid sample 21 is suppliedto a plasma generator 30 from a sample introducer 20. Compounds andatoms existing in such fine droplets are decomposed and ionized inplasma 32. Sample ions obtained as a result are transferred to a massanalyzer 40. The mass analyzer 40 is configured such that the pressureis gradually decreased along the flow of the sample ions by using aturbo molecular pump, a rotary vacuum pump, and the like (not shown).

The sample ions are drawn to an ion lens system 43 through an orifice inan interface including a sampling cone 41 and a skimmer cone 42. Then,the sample ions are converged in a quadrupole mass spectrometer 45through a collision/reaction cell 44. The quadrupole mass spectrometer45 separates the sample ions based on a mass-to-charge ratio. As adevice for separating the sample ions other than the quadrupole massspectrometer, there also exist mass spectrometers of, for example,electric/magnetic sector type, flight time type, or ion trap type. Theseparated ions are measured by a detector 46. Such ICP-MS apparatus asthe above provides means for performing a simultaneous multi-elementanalysis on most of the elements in the periodic table, and thus a massspectrum can easily be obtained. In addition, such ICP-MS apparatusexhibits an excellent sensitivity such that element concentrations canbe quantified at a level of one trillionth (ppt).

In FIG. 1, the mass analyzer 40 is illustrated as a mass analysis deviceusing a quadrupole mass spectrometer. However, the mass analyzer 40 canalso be an atomic emission spectrometer for observing emission spectrumof induced plasma generated in the plasma generator 30. The ICPspectrometric apparatus configured in this manner is generally referredto as an ICP-OES (Inductively Coupled Plasma—Optical EmissionSpectrometry) apparatus or an ICP-AES (Inductively Coupled Plasma—AtomicEmission Spectrometry) apparatus.

In FIG. 1, a pressure-adjusted gas from a gas source 10 is supplied to agas line 13 at a flow rate of from approximately 8 SLM to 27 SLM. Thegas of the gas source is mainly an inert gas such as an argon (Ar) gas,nitrogen (N₂) gas, and helium (He) gas, but can be a hydrogen (H₂) gas,an oxygen (O₂) gas, and the like, or a mixed gas thereof according tothe usage. In FIG. 1, only one gas source is shown, but a plurality ofgas sources can also be provided. In this case, the gas of each gassource can be the same or different.

The gas line 13 from the gas source 10 is referred to as a source gasline in the present specification, and is branched or divided into gaslines 61 and 63 through a connector 60. When a plurality of gas sourcesexist, the gas lines 61 and 63 can be respectively connected to each ofthe gas sources. The gas line 61 is connected to a gas filter 50. Thegas filter 50 will be explained later. The gas flowing in the gas line61 is removed of impurities contained therein by the gas filter 50, andis supplied to a gas line 62. The gas line 62 is, as is shown in FIG. 1,branched into a gas line 15 for a carrier gas and a gas line 16 for amake-up gas through a connector 64. A gas flow rate controller 14 isprovided in each of the gas lines 15 and 16. The gas flow ratecontroller can be a mass flow controller (MFC).

The gas line 15 is connected to a nebulizer 22 in the sample introducer20, and the gas line 16 is connected to an end cap 23. In addition, theliquid sample 21 containing an analyte is also supplied to the nebulizer22. As shown, the nebulizer 22 is connected to a spray chamber 24through the end cap 23. The nebulizer 22 mixes the carrier gas from thegas line 15 with the liquid sample 21, and sprays the mixture. Themake-up gas passes through a surrounding of a tip of the nebulizer 22,assists the delivery of the nebulized sample, and optimizes theionization condition of analysis object elements in the plasma. Thenebulized sample is removed of large droplets by passing through thespray chamber 24 together with the carrier gas and the make-up gas, andis sent into an ICP torch 31 in the plasma generator 30 as the injectorgas (aerosol).

The gas line 63 is branched into a gas line 17 for a plasma gas and agas line 18 for an auxiliary gas through a connector 65. In the gaslines 17 and 18, a gas flow rate controller 14 is provided. The gas flowrate controller can be a mass flow controller (MFC). According to acommand from a controller of the ICP analysis apparatus or a computer,etc. (not shown), each MFC 14 measures the mass flow rate of the gasflowing in each of the gas lines 15 to 18, and controls the flow rate.

The gas lines 13, 15 through 18, and 61 through 63 are each a tube madeof, for example, a stainless steel or a resin, and the inner diameter ofthe tube is generally from about 0.5 mm to 8 mm in diameter. From thestandpoint of eliminating an extremely trace amount of impurities, suchas organic silicon compounds, organic sulfur compounds, or organichalogen compounds, a tube made of a stainless steel is more preferred.The ICP torch 31 which is also referred to as a plasma torch has atriple-tube structure of quartz, and has an inner tube to which theinjector gas is introduced, an outer tube which is outside the innertube, and an outermost tube which is further outside the outer tube. Theauxiliary gas is introduced to the outer tube by the gas line 18, andthe plasma gas is introduced to the outermost tube by the gas line 17.

At a tip of the ICP torch 31, a work coil (not shown) which provides anenergy for generating the plasma 32 is disposed, and connected to a highfrequency power source (not shown). With the auxiliary gas and theplasma gas being provided to the ICP torch 31, the high frequency powercan be applied to make the plasma 32 in a lighting state. Thetemperature of the plasma reaches from a several 1,000 K to a 10,000 K.The plasma gas is used to generate and maintain plasma. In addition, theplasma gas also functions to cool down the ICP torch 31. The auxiliarygas plays a role of protecting the inner tube and the outer tube of theICP torch 31 by shifting a position where the plasma 32 is generatedtoward a downstream side. Further, there is a case where the auxiliarygas does not need to be flown depending on the form of the plasma torch.The injector gas containing fine droplets of the liquid sample isprovided from the inner tube. As described above, compounds and atomsexisting in such fine droplets are decomposed and ionized in the plasma32.

As described above, industrial gases supplied by gas providers maycontain an extremely trace amount of impurities, or may be contaminatedby piping, and the like. It is desirable that the gas used in particularfor a plasma spectrometric apparatus such as an ICP-MS apparatus, anICP-AES apparatus, a MIP-MS apparatus, and a MIP-AES apparatus does notcontain impurities such as silicon (Si), sulfur (S), phosphorus (P),boron (B), krypton (Kr), xenon (Xe), chlorine (Cl), and bromine (Br).The above gas filter 50 is a gas purifier configured to remove suchimpurities.

For example, such gas purifier as the above has a cylindrical structuremade of metal provided with an inlet for gas flowing in and an outletfor purified gas flowing out, and a purification element for purifyingthe gas is filled therein. As the purification element, for impuritiesof organic compounds such as organic silicon compounds, organic sulfurcompounds, or organic halogen compounds, it is effective to use, forexample, an absorbent such as activated carbon or zeolite, or an alloycalled a getter, which is like a zirconium alloy that absorbs impuritiesin the gas. In addition, impurities such as hydrogen sulfide can beremoved by causing a chemical reaction with a metal oxide such as acopper oxide. A gas purifier like this has a service life whose lengthsignificantly differs depending on the substance to be removed, but ingeneral, it has an ability of continuously removing impurities from anargon gas of 99.999% purity flowing at 1 SLM for from 1000 to 100,000hours.

Further, the gas filter 50 can be in a form of a cartridge. The gasfilter 50 can be replaceably connected to the gas lines 61 and 62 byusing a connector, and the like (not shown). In FIG. 1, one gas filter50 is shown. However, as is indicated in the alternative configurationsof FIG. 2A and FIG. 2B, gas filters 51 and 52 may also be provided inthe gas line 15 for the carrier gas and the gas line 16 for the make-upgas, respectively. In FIG. 2A, the gas filters 51 and 52 are provided onthe inlet side of the gas flow rate controller 14. However, the gasfilters 51 and 52 may also be provided on the outlet side of the gasflow rate controller 14 as shown in FIG. 2B. In addition, in FIG. 1,FIG. 2A and FIG. 2B, one gas filter is provided in each gas line, but aplurality of gas filters can also be connected serially or in parallelin order to remove a wide variety of impurities.

FIG. 5 shows a result obtained experimentally on the capability of a gaspurifier itself to remove a Si impurity in consideration of a case wherethe gas filter 50 is configured as a gas purifier. The horizontal axisof the graph indicates a flow rate (SLM) of the gas (including the Siimpurity) flowing into the gas filter. The left vertical axis of thegraph indicates a value obtained by converting a concentration of the Siimpurity in the gas to a concentration in the sample solution. The rightvertical axis of the graph indicates a passage rate at which the Siimpurity passes through the gas filter without being removed. The curveA indicates a concentration of the Si impurity introduced into the gasfilter in terms of a concentration in the sample. The curve B indicatesa concentration of the Si impurity that passed through the gas filter interms of a concentration in the sample. The curve C indicates a passagerate at which the Si impurity passes through the gas filter. The passagerate is obtained by dividing the value B by the value A.

It is obvious from FIG. 5 that the higher the flow rate of the gasflowing in, the more difficult to remove the Si impurity contained inthe gas by the gas filter. For example, when comparing the leftmostpoint corresponding to the gas flow rate of 1 SLM with the rightmostpoint corresponding to the gas flow rate of 20 SLM in the graph C, thepassage rate differs by approximately three digits. That is, the gasfilter can effectively remove impurities when the gas flow rate is low(e.g., 1 SLM).

In the ICP-MS apparatus 100 shown in FIG. 1, the gas flow rate in thegas line 15 for the carrier gas is generally from approximately 0.2 to1.5 SLM, preferably from approximately 0.5 to 1.0 SLM, and more suitablyapproximately 0.7 SLM. The gas flow rate in the gas line 16 for themake-up gas is from approximately 0.0 to 1.5 SLM, preferably fromapproximately 0.0 to 1.0 SLM, and more preferably approximately 0.3 SLM.

Further, the gas flow rate in the gas line 17 for the plasma gas isgenerally from approximately 8 to 23 SLM, and preferably fromapproximately 12 to 20 SLM. The gas flow rate in the gas line 18 for theauxiliary gas is generally from approximately 0.0 to 2.0 SLM, andpreferably approximately 1 SLM. It is considered that the gas flow ratein the gas line 62 is approximately 1 SLM, and the gas flow rate in thegas line 63 is from approximately 13 to 21 SLM.

As described above, the gas filter can effectively remove impuritieswhen the flow rate of the gas is low (e.g., 1 SLM). In addition, ananalysis result of the plasma spectrometric apparatus is less affectedby impurities contained in the plasma gas and the auxiliary gas thanimpurities contained in the injector gas. In the present invention, thegas filter 50 is used only in the gas line 62 having a low gas flowrate, and not used in the gas line 63 having a high gas flow rate. Bysuch configuration, it is possible to effectively remove the impuritiescontained in the carrier gas and the make-up gas constituting theinjector gas while effectively using the filtering capability of the gasfilter 50. This also reduces background noise and the like attributed tothe impurities, and improves the analytical ability of the plasmaspectrometric apparatus. Further, it also prevents the life of the gasfilter from being shortened.

In the above explanation, the gas filter 50 is used only in the gas line62. However, if the gas flow rate in the gas line 18 for the auxiliarygas is low, the gas line 18 for the auxiliary gas may be branched ordivided from the gas line 62 instead of the gas line 63. That is, inaddition to the injector gas, the auxiliary gas may also be purified bythe gas filter 50. This allows to further improve the analytical abilityof the plasma spectrometric apparatus.

In the ICP-MS apparatus 100 as shown in FIG. 1, when the liquid sample21 contains many substances that are not the analysis objects (e.g.,sodium chloride, magnesium chloride, etc.) such as sea water, a dilutiongas for diluting the injector gas may be supplied from a gas addinginlet 27. The dilution gas can be an argon gas, and supplied to the gasadding inlet 27 through a flow rate controller such as the flow ratecontroller 14 after being branched from the gas line 62. The flow rateof the dilution gas is from 0 to approximately 1 SLM, and preferablyfrom approximately 0.3 to approximately 0.8 SLM.

In addition, when a solvent of the liquid sample 21 is an organicsolvent, an oxygen-containing gas may also be added as an option gasfrom the gas adding inlet 27 to the injector gas. When theoxygen-containing gas is introduced as the option gas, decomposition oforganic matters in the plasma 32 is accelerated and accumulation ofundecomposed organic matters, soot, and the like to the torch 31, thesampling cone 41, the skimmer cone 42, and the ion lens system 43 can beinhibited, thereby preventing the analytical performance from beinglowered. The option gas can be supplied to the gas adding inlet 27 froma different gas source (not shown) through a gas filter such as the gasfilter 50. In the present specification, a gas line delivering theoption gas is referred to as an optional gas line. A flow ratecontroller such as the flow rate controller 14 can also be provided inthe optional gas line.

The option gas can be an oxygen gas, an argon-containing oxygen gas, anitrogen-containing oxygen gas, a helium-containing oxygen gas, andmixtures thereof. The flow rate of the option gas is from 0 toapproximately 1 SLM, and preferably from approximately 0.1 toapproximately 0.5 SLM. In some cases, both the dilution gas and theoption gas can be supplied to the gas adding inlet 27.

When the present invention is applied to a MIP analysis apparatus, theplasma generator 30 shown in FIG. 1 is replaced by a system generatingmicrowave induced plasma (MIP), and the plasma gas and the auxiliary gasare supplied to the plasma generator 30 in the same manner as in the ICPanalysis apparatus. A system generating MIP is, for example, explainedin Patent Literature 3.

As an alternative of the ICP-MS apparatus 100 of FIG. 1, the sampleintroducer 20 of FIG. 1 can be replaced by a gas chromatograph 300 shownin FIG. 3. In this case, the carrier gas or the make-up gas in the gaschromatograph can be supplied from a different gas source (not shown). Agas filter such as the gas filter 50 shown in FIG. 1 can be provided ina gas line for the carrier gas or the make-up gas from the different gassource, and can purify the carrier gas or the make-up gas.

The carrier gas in the gas chromatograph can generally be a helium (He)gas, an argon (Ar) gas, a hydrogen (H₂) gas, a nitrogen (N₂) gas, andthe like. As an alternative, the carrier gas in the gas chromatograph300 may be supplied through a gas line 15′ as the gas line 15 shown inFIG. 1. In addition, the make-up gas in the gas chromatograph 300 can besupplied through a gas line 16′ as the gas line 16 shown in FIG. 1. Themake-up gas is a gas for achieving an optimum ionization condition indetecting an analyte element in the mass analyzer 40, and the range ofthe flow rate is the same as that of the carrier gas or the make-up gasused in a normal ICP analysis apparatus. Therefore, in an aspect inwhich the carrier gas is supplied using a different gas source, themake-up gas for the gas chromatograph 300 can be supplied through thegas line 15 or the gas line 16 as shown in FIG. 1. As is shown in FIG.3, an output of the gas chromatograph 300 is connected to an injector314 through a transfer line 313, and the injector 314 is inserted in aplasma torch 31′ as an inner tube.

In FIG. 3, a sample 21′ is introduced to a column 310 together with thecarrier gas in the gas line 15′. The introduced sample is separated byeach component when passing through the column 310. The make-up gassupplied through the gas line 16′ passes through a preheating tube 311,which adjusts the temperature of the make-up gas. The carrier gascontaining the sample separated by the column 310 and thetemperature-adjusted make-up gas are mixed to produce the injector gas.The injector gas is introduced to the inner tube of the plasma torch 31′as shown in FIG. 1 through the transfer line 313 and the injector 314.The temperatures of the column 310 and the preheating tube 311 areadjusted by an oven. Further, the temperatures of the transfer line 313and the injector 314 are adjusted by a heater and the like (not shown).

As yet another alternative, the sample introducer 20 of FIG. 1 can bereplaced by a laser ablation device 400 shown in FIG. 4. In this case,the gas lines 15 and 16 of FIG. 1 are connected to gas lines 15″ and 16″shown in FIG. 4, respectively. In addition, the portion A shown in FIG.1 and the portion A shown in FIG. 4 are connected. In FIG. 4, a solidsample 420 is placed in an ablation cell 410. A laser light from a laser450 is irradiated to the surface of the solid sample 420 thorough a halfmirror 440 and a lens and the like (not shown). By a CCD camera 430,portions to be analyzed in the sample can be observed. The sampleevaporated and particulated by the irradiated laser light is dischargedfrom the ablation cell 410 by the carrier gas, but in some cases, gassuch as a helium (He) gas is added to the carrier gas for the purpose ofoptimizing the ablation condition of the sample. Then, the dischargedsample is mixed with the make-up gas to become the injector gas. Theinjector gas is introduced to the inner tube of the plasma torch 31shown in FIG. 1.

EXAMPLES

The impact on an analysis result by applying the present invention in anICP-MS apparatus was experimentally verified. In the present experiment,an ICP-MS/MS apparatus such as that described in Patent Literature 4 wasused in a gas supplying configuration shown in FIG. 1. In this case, achamber was extended such that a quadrupole mass filter could bedisposed between the ion lens system 43 and the collision/reaction cell44 in the mass analyzer 40 of FIG. 1. In addition, in the ICP-MS/MSapparatus used in the experiment, a collision/reaction cell providedwith an octupole was used.

The condition of the experiment was as follows. For gas as a gas source,an argon gas of 99.999% purity commercially available from Taiyo NipponSanso Corporation as an industrial gas was used. Then, the argon gas wasused each as a plasma gas, an auxiliary gas, a carrier gas, and amake-up gas, having the flow rate of 15.0 SLM, 0.90 SLM, 0.70 SLM, and0.37 SLM, respectively. For a gas filter, RMSH-2 commercially availablefrom Agilent Technologies was used. As a high frequency power forgenerating plasma, a power of 1500 W was applied to the work coil. Theintroduction speed of the sample solution was approximately 200 μL/min(0.2 g/min), and the temperature of the spray chamber was 2° C. Inaddition, the distance between the downstream end of the work coil tothe tip of the sampling cone was 4 mm. As a cell gas, a helium (He) gaswas introduced at a flow rate of 1 SCCM, and a 10% ammonia (10% NH3/He)gas diluted by helium was introduced at a flow rate of 0.5 SCCM to thecollision/reaction cell. Along the flow of sample ions, themass-to-charge ratio (m/z) for passing through the first quadrupole massfilter was set to 28, and the m/z for passing through the secondquadrupole mass filter was set to 44, and the ICP-MS/MS apparatus wasoperated as MS/MS mode. In this mode, after a Si ion (Si⁺, m/z=28)generated in the plasma passes through the first quadrupole mass filter,it collides and reacts with an ammonia molecule in thecollision/reaction cell provided with the octopole, and becomes SiNH₂ ⁺(m/z=44), which then reaches to a detector and is converted to anelectric signal after passing through the second quadrupole mass filter.

The experiment results are shown in FIG. 6A through FIG. 6C. FIG. 6Ashows a background equivalent concentration (BEC) and a signal intensityof a Si element when continuously operating, without using the gasfilter 50 as in the conventional ICP-MS apparatus shown in FIG. 7, suchICP-MS apparatus for 36 hours. In this graph, the horizontal axisindicates the time (h), the left vertical axis the signal intensity, andthe right vertical axis the BEC. The graph of FIG. 6B shows a BEC and asignal intensity of a Si element when continuously operating, by usingthe gas filter 50 as in the ICP-MS apparatus of FIG. 1, the ICP-MSapparatus for 36 hours based on the same condition as that of FIG. 6A.The horizontal axes of the graphs in FIG. 6A and FIG. 6B and thevertical axes thereof are in the same range, respectively.

In the graphs of FIG. 6A and FIG. 6B, graph (1) shows a signal intensity(the signal intensity of the background) (counts/sec) when ultrapurewater (deionized water, or DIW) is introduced, and graph (2) shows asignal intensity (counts/sec) when a sample containing Si of 1 ppb (1μg/L) is introduced into ultrapure water. Here, by subtracting (1) from(2), a net signal intensity relative to Si per 1 ppb, that is, apparatussensitivity (counts/(sec·ppb)), can be obtained. Graph (3) can beobtained by dividing the signal intensity (1) of the background at thetime of introducing ultrapure water by the apparatus sensitivity((2)-(1)). The value shown by graph (3) indicates a background signalintensity as a concentration in a solution (ppb), and is referred to asa BEC (background equivalent concentration). The BEC value is anumerical value serving as a reference for at how low a level ananalysis can be conducted in an analytical apparatus, and the smallerthe value is, the lower the concentration level at which the analysis ispossible.

The graph of FIG. 6A indicates that the background changes over time,showing fluctuations in a range between several 100 ppt and several 10ppb in terms of BEC. Such changes are considered to be caused by thechanges in the temperature of the piping or the flow rate of the gasflowing therein, the industrial gas lot, or the individual difference ina compressed gas cylinder contamination. Under this condition, it ispossible to detect and quantify Si in a concentration range of several100 ppb; however, it is not possible to conduct an analysis at a levelof several 10 ppb, let alone an analysis at a level of ppb. On the otherhand, in the graph of FIG. 6B, unlike the graph of FIG. 6A, the BECvalue is stable over approximately 36 hours, and the BEC value of Si isrestrained so as to be equal to or less than several 100 ppt. Thus, itis made possible to detect and quantify Si in a concentration rangelower than the level of several ppt.

The average of BEC values of Si shown in FIG. 6A and FIG. 6B are 2.97ppb and 0.32 ppb. FIG. 6C shows these average values in a bar graph. BECrepresents a concentration of a measurement object element that gives asignal intensity equivalent to the background intensity. In other words,lowering of a BEC value signifies a reduction in the background noiseattributed to impurities. Therefore, it was verified that removing ofimpurities contained in the carrier gas and the make-up gas by the gasfilter 50 according to the present invention reduced, in a continuous36-hour operation, the fluctuation in the background level and thebackground noise.

Below shows exemplary embodiments comprising combinations of variousconfiguration requirements of the present invention.

1. A plasma spectrometric apparatus comprising a sample introducer forproducing and delivering an injector gas containing an analyte sample, aplasma generator for generating plasma into which the injector gas isintroduced, and an analyzer disposed subsequent to the plasma generatorfor analyzing the analyte sample, wherein the plasma spectrometricapparatus further comprises: a first gas line for supplying gas to saidsample introducer; a second gas line for supplying gas to said plasmagenerator; and a filter located in said first gas line for removingimpurities contained in the gas.

2. The plasma spectrometric apparatus according to the above 1, whereinsaid first gas line and said second gas line are branched from a sourcegas line.

3. The plasma spectrometric apparatus according to the above 1 or 2,wherein the flow rate through said first gas line is smaller than theflow rate through said second gas line.

4. The plasma spectrometric apparatus according to any one of the above1 to 3, wherein said filter is a gas purifier.

5. The plasma spectrometric apparatus according to any one of the above1 to 4, wherein said first gas line is provided with a gas flow ratecontroller between said sample introducer and said filter.

6. The plasma spectrometric apparatus according to any one of the above1 to 5, wherein said first gas line branches into a third gas line and afourth gas line, one delivering a carrier gas and the other delivering amake-up gas to said sample introducer.

7. The plasma spectrometric apparatus according to the above 6, whereinsaid filter is located in each of said third gas line and said fourthgas line.

8. The plasma spectrometric apparatus according to any one of the above1 to 7, wherein said second gas line branches into a fifth gas line anda sixth gas line, one delivering a plasma gas and the other deliveringan auxiliary gas to said plasma generator.

9. The plasma spectrometric apparatus according to any one of the above1 to 7, wherein a seventh gas line for delivering an auxiliary gas tosaid plasma generator is branched from said first gas line.

10. The plasma spectrometric apparatus according to any one of the above1 to 9, wherein an eighth gas line for delivering a dilution gas to saidsample introducer is branched from said first gas line.

11. The plasma spectrometric apparatus according to any one of the above1 to 10, further comprising: an optional gas line for supplying anoption gas to said sample introducer, and a second filter located insaid optional gas line for removing impurities contained in the optiongas.

12. The plasma spectrometric apparatus according to any one of the above1 to 11, wherein the gas supplied through each of said first and saidsecond gas lines is selected from the group consisting of argon,nitrogen, helium, hydrogen, and mixtures thereof.

13. The plasma spectrometric apparatus according to the above 11,wherein said option gas is an oxygen-containing gas selected from thegroup consisting of oxygen, argon-containing oxygen, nitrogen-containingoxygen, helium-containing oxygen, and mixtures thereof.

14. The plasma spectrometric apparatus according to any one of the above1 to 13, wherein said sample introducer comprises a nebulizer forproducing said injector gas by mixing said analyte sample with the gasfrom said first gas line.

15. The plasma spectrometric apparatus according to any one of the above1 to 13, wherein said injector gas is the output from a gaschromatograph.

16. The plasma spectrometric apparatus according to any one of the above1 to 5, wherein, said injector gas is the output from a gaschromatograph, said first gas line delivers one of a carrier gas and amake-up gas to the gas chromatograph, the other gas is delivered to thegas chromatograph through a further gas line, and a further filter isprovided in the further gas line for removing impurities from the othergas.

17. The plasma spectrometric apparatus according to any one of the above1 to 13, wherein said injector gas is the output from a laser ablationdevice.

18. The plasma spectrometric apparatus according to any one of the above1 to 17, wherein said plasma generator comprises a plasma torch forreceiving the gas from said second gas line to generate plasma intowhich the injector gas is introduced.

19. The plasma spectrometric apparatus according to any one of the above1 to 18, wherein said plasma generator uses inductively coupled plasmaor microwave induced plasma.

20. The plasma spectrometric apparatus according to any one of the above1 to 19, wherein said analyzer uses a mass spectrometer or an atomicemission spectrometer.

21. In a plasma spectrometric apparatus comprising a sample introducerfor producing and delivering an injector gas containing an analytesample, a plasma generator for generating plasma into which the injectorgas is introduced, and an analyzer disposed subsequent to the plasmagenerator for analyzing the analyte sample, a method for reducingbackground intensity in measurements, comprising: supplying a first gasto said sample introducer through a filter for removing impurities; andsupplying a second gas to said plasma generator without filtering.

22. The method according to the above 21, wherein the flow rate of saidfirst gas is smaller than the flow rate of said second gas.

23. The method according to the above 21 or 22, wherein said first gasis used as a carrier gas and a make-up gas.

24. The method according to any one of the above 21 to 23, wherein saidsecond gas is used as a plasma gas and an auxiliary gas.

25. The method according to the above 21 or 22, wherein said first gasis used as a carrier gas, a make-up gas, and an auxiliary gas.

26. The method according to the above 21 or 22, wherein said first gasis used as a carrier gas, a make-up gas, and a dilution gas.

27. The method according to any one of the above 21 to 26, wherein saidfirst gas and said second gas are supplied from the same gas source.

28. The method according to any one of the above 21 to 27, wherein saidfilter is a gas purifier.

29. The method according to the above 21, further comprising supplyingan option gas to said sample introducer through a second filter forremoving impurities.

30. The method according to any one of the above 21 to 29, wherein saidplasma generator uses inductively coupled plasma or microwave inducedplasma.

31. The method according to any one of the above 21 to 30, wherein saidanalyzer uses a mass spectrometer or an atomic emission spectrometer.

EXPLANATION OF REFERENCE NUMERALS

-   -   10: Gas source    -   13, 15, 15′, 15″, 16′, 16″, 17, 18, 61 to 63: Gas line    -   14: Gas flow rate controller    -   20: Sample introducer    -   21, 21′: Sample    -   22: Nebulizer    -   30: Plasma generator    -   31, 31′: Plasma torch    -   40: Mass analyzer    -   50, 51, 52: Gas filter    -   100, 100′: ICP-MS apparatus    -   300: Gas chromatograph    -   400: Laser ablation device

It will be understood that various aspects or details of the inventionmay be changed without departing from the scope of the invention.Furthermore, the foregoing description is for the purpose ofillustration only, and not for the purpose of limitation—the inventionbeing defined by the claims.

What is claimed is:
 1. A plasma spectrometric apparatus comprising a sample introducer for producing and delivering an injector gas containing an analyte sample, a plasma generator for generating plasma into which the injector gas is introduced, and an analyzer disposed subsequent to the plasma generator for analyzing the analyte sample, wherein the plasma spectrometric apparatus further comprises: a first gas line for supplying gas to the sample introducer; a second gas line for supplying gas to said plasma generator; and a filter located in the first gas line for removing impurities contained in the gas to be supplied to the sample introducer.
 2. The plasma spectrometric apparatus of claim 1, wherein said first gas line and said second gas line are branched from a source gas line.
 3. The plasma spectrometric apparatus of claim 1, wherein the flow rate through said first gas line is smaller than the flow rate through said second gas line.
 4. The plasma spectrometric apparatus of claim 1, wherein said filter is a gas purifier.
 5. The plasma spectrometric apparatus of claim 1, wherein said first gas line branches into a third gas line and a fourth gas line, one delivering a carrier gas and the other delivering a make-up gas to said sample introducer.
 6. The plasma spectrometric apparatus of claim 5, wherein said filter is located in each of said third gas line and said fourth gas line.
 7. The plasma spectrometric apparatus of claim 1, wherein said second gas line branches into a fifth gas line and a sixth gas line, one delivering a plasma gas and the other delivering an auxiliary gas to said plasma generator.
 8. The plasma spectrometric apparatus of claim 1, wherein a seventh gas line for delivering an auxiliary gas to said plasma generator is branched from said first gas line.
 9. The plasma spectrometric apparatus of claim 1, wherein an eighth gas line for delivering a dilution gas to said sample introducer is branched from said first gas line.
 10. The plasma spectrometric apparatus of claim 1, further comprising: an optional gas line for supplying an option gas to said sample introducer, and a second filter located in said optional gas line for removing impurities contained in the option gas, wherein said option gas is an oxygen-containing gas selected from the group consisting of oxygen, argon-containing oxygen, nitrogen-containing oxygen, helium-containing oxygen, and mixtures thereof.
 11. The plasma spectrometric apparatus of claim 1, wherein the gas supplied through each of said first and said second gas lines is selected from the group consisting of argon, nitrogen, helium, hydrogen, and mixtures thereof.
 12. The plasma spectrometric apparatus of claim 1, wherein said sample introducer comprises a nebulizer for producing said injector gas by mixing said analyte sample with the gas from said first gas line.
 13. The plasma spectrometric apparatus of claim 1, wherein said injector gas is the output from a gas chromatograph.
 14. The plasma spectrometric apparatus of claim 1, wherein said injector gas is the output from a laser ablation device.
 15. The plasma spectrometric apparatus of claim 1, wherein said plasma generator comprises a plasma torch for receiving the gas from said second gas line to generate plasma into which the injector gas is introduced. 